Zak and Zelda Williams paid tribute to the actor with poignant posts on social media

Robin Williams’ children are remembering him and what he stood for.

On Friday, Robin’s son Zak Williams and daughter Zelda Williams both paid tribute to their father on social media, celebrating what would have been his 72nd birthday. The actor died in 2014 at age 63.

“Happy 72nd Dad! Was remembering how much I used to love that look you’d give. That look with a mischievous, loving grin that your friends and loved ones knew so well. Joyous and curious and wondrous,” Zak captioned a throwback photo on Instagram that showed his father wearing headphones and smiling.

“Miss you and love you forever!” the 40-year-old added.

In her tribute, Zelda, 33, tweeted about how she believed Robin would have supported the current writers and actor’s strike alongside a photo of the late actor joining the New York picket line in the 2007 strike.

“Happy birthday to Poppo, who definitely would’ve been out there fighting the good fight for art and artists today and always,” Zelda wrote in her caption.

In the photo, Robin held up a sign that said ‘SAG WGA ON STRIKE’ as he stood alongside fellow protestors.

The Jumanji star was outspoken in advocating for screenwriters’ rights during the strike in 2007. “This is not about millionaire screenwriters. They don’t need to be on strike. This is not about me, I’m fine,” Robbins told The Hollywood Reporter during the protests at the time. “This is about a large amount of people who are simply trying to get their fair share.”

“You want to resolve it for their sake and get everybody back working and find a way to share it,” the late actor had added.

Zak is the eldest son of Robin and his first wife Valerie Velardi. Zelda and brother Cody Williams, 31, are Robin’s children from his second marriage to Marsha Garces Williams.

Robin Williams Zelda williams Zachary Williams

Robin’s 72nd birthday was Friday July 21.ETHAN MILLER/GETTY; STEVE ZAK PHOTOGRAPHY/WIREIMAGE

Robin’s birthday comes ahead of the ninth anniversary of his death next month.

In February, his former costar Sally Field reflected on her time getting to know the late actor.

During the PEOPLE & Entertainment Weekly Red Carpet Live, the actress, 76, recalled making the 1993 comedy Mrs. Doubtfire with the comedian.

“What you think about immediately is Robin. There isn’t a moment of it that’s not filled with my love and joy at being in his presence,” she told PEOPLE. “I mean, Robin was Robin. He was everything he seemed to be: a generous, loving, sweet, geniously talented man.”

“We all miss him,” added Field. “He should be growing old like me, for God’s sakes. I hate it that he isn’t here.”